Model and Image based Investigation into Mechanisms of Olive Dieback caused by Xylella fastidiosa biofilms

Xylella fastidiosa (X. fastidiosa) is a bacterium that colonises internal plant vascular networks causing pathogenic effects on several commercially important crops (e.g. olives, grapes, coffee, etc.). Despite a growing research effort since the recent detection of X. fastidiosa in Europe, the exact processes leading to X. fastidiosa disease symptoms are not fully understood due to difficulties in observing internal plant structures. Our goal is to utilise models to elucidate fundamental processes that lead to olive quick decline syndrome, the disease responsible for the devastating olive decline in Apulia, Southern Italy. We endeavour to do this by developing a fundamental mathematical modelling framework describing within-host biofilm development, and the resulting water-stresses that ultimately inhibit plant functionality and development. We have begun work on developing a fluid mechanics model that invokes a polymer-physical description of X.fastidiosa biofilm formation dynamics. Our approach is centred on the assumption that the biofilm structure is determined by the arrangement of extracellular polysaccharide (EPS) molecules. We have also produced X-ray Computed Tomography (XCT) images of both resistant and susceptible olive cultivars to determine possible morphological differences between the vascular networks of the cultivars. Additionally, these images provide detailed geometries for our models, with which we will investigate the effect of xylem geometry on resistance. Preliminary modelling results of EPS dominant biofilm formation characterise biofilm coalescence in a consistent manner with early microfluidic controlled experiments and require fewer empirical assumptions. We hope our work will improve the understanding of possible cultivar resistance mechanisms to enable informed breeding and effective replanting in Apulia, and that model simulations will provide insights for improving the efficiency of current sampling techniques.<br